title: Evolution of genetic switch complexity.
abstract: The circuitry of the phage λ genetic switch determining the outcome of lytic or lysogenic growth is well-integrated and complex, raising the question as to how it evolved. It is plausible that it arose from a simpler ancestral switch with fewer components that underwent various additions and refinements, as it adapted to vast numbers of different hosts and conditions. We have recently identified a new class of genetic switches found in mycobacteriophages and other prophages, in which immunity is dependent on integration. These switches contain only three genes (integrase, repressor andcro) and represent a major departure from the λ-like circuitry, lacking many features such asxis,cIIandcIII. These small self-contained switches represent an unrealized, elegant circuitry for controlling infection outcome. In this addendum, we propose a model of possible events in the evolution of a complex λ-like switch from a simpler integration-dependent switch.
authors.affiliation: Department of Biological Sciences; University of Pittsburgh; Pittsburgh, PA USA.
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Broussard
authors.forename: Graham F
authors.initials: GF
authors.lastname: Hatfull
keywords: bistable; genetic circuits; genetic switch; integration-dependent immunity; lytic and lysogenic growth